Design of a Cognitive VLC Network with Illumination and Handover Requirements

In this paper, we consider a cognitive indoor visible light communications (VLC) system, comprised of multiple access points serving primary and secondary users through the orthogonal frequency division multiple access method. A cognitive lighting cell is divided into two non-overlapping regions that distinguish the primary and secondary users based on the region they are located in. Under the assumption of equal-power allocation among subcarriers, each region is defined in terms of its physical area and the number of allocated subcarriers within that region. In this paper, we provide the lighting cell design with cognitive constraints that guarantee fulfilling certain illumination, user mobility, and handover requirements in each cell. We further argue that, under some conditions, a careful assignment of the subcarriers in each region can mitigate the co-channel interference in the overlapping areas of adjacent cells. Numerical results depict the influence of different system parameters, such as user density, on defining both regions. Finally, a realistic example is implemented to assess the performance of the proposed scheme via Monte Carlo simulations

High energy interactions on nuclei

Multihadron production and coherent or semicoherent reactions on nuclei allow information about such intriguing topics as space-time development of particle production and interactions of resonances with nucleons. Some of the latest results are here summarized, with particular emphasis on the coherent and semicoherent channels, in connection with the criticisms and suggestions recently developed regarding the so called sigma /sub 2/ cross-section (for the interactions of resonances with nucleons), as it is obtained from the A dependence of diffractive production on nuclei. (34 refs)

Local Positioning Services on IEEE 802.11 Networks

This paper deals with localization services in IEEE 802.11 networks, for indoor environment. The proposed solution processes the Time Of Arrival of location packets sent by a Mobile Terminal, that makes access in a IEEE 802.11 network. A set of Location Supporting Nodes and a Location Support Server composes an indoor location services architecture. A fully compatible IEEE 802.11 Localization Services protocol supporting data exchange related to both TOA measurement and processing is reported. Simulation results show the method efficiency in both IEEE 802.11 PCF and DCF modes. Assessment of the maximum number of users for which location services can be provided is also reported. Since high localization accuracy requires large bandwidth, a broadband antenna for LSN and LSS was designed. The related results are reported in the second part of the paper. The antenna works at 5.0 GHz (centre frequency) in broadband mode and is matched on the wireless operating frequencies with a percentage more than 8% (1:1.5 VSWR)

Shielding and Radiation Characteristics of Cylindrical Layered Bianisotropic Structures

In this paper we propose an analytical study in the spectral domain of cylindrical layered structures filled with general bianisotropic media and fed by a 3D electric source. The integrated structure is characterized in terms of transmission matrices leading to an equivalent circuit representation of the whole multilayered structure. Within the framework of this two-port formalism, we present a new contribution to the computation of the Green's function arising in the analysis of multilayered conformal integrated antennas loaded with general bianisotropic materials. We also propose an analytical study of the shielding effectiveness of general bianisotropic materials located in multilayered, cylindrical configuration. The expression of the shielded fields sustained both by plane wave and arbitrary sources is obtained in a closed analytical form. Numerical results are also presented showing effects of electromagnetic parameters on radiation pattern, matching properties and radar cross section of the integrated structure

Enhanced transmission through a subwavelength aperture using metamaterials

We report an enhanced transmission through a single circular subwavelength aperture that is incorporated with a split ring resonator (SRR) at the microwave regime. Transmission enhancement factors as high as 530 were observed in the experiments when the SRR was located in front of the aperture in order to efficiently couple the electric field component of the incident electromagnetic wave at SRR's electrical resonance frequency. The experimental results were supported by numerical analyses. The physical origin of the transmission enhancement phenomenon was discussed by examining the induced surface currents on the structures

The longtime behavior of a nonlinear Reissner-Mindlin plate with exponentially decreasing memory kernels

In this paper we investigate the longtime behavior of the mathematical model of a homogeneous viscoelastic plate based on Reissner–Mindlin deformation shear assumptions. According to the approximation procedure due to Lagnese for the Kirchhoff viscoelastic plate, the resulting motion equations for the vertical displacement and the angle deflection of vertical fibers are derived in the framework of the theory of linear viscoelasticity. Assuming that in general both Lame’s functions, λ and μ, depend on time, the coupling terms between the equations of displacement and deflection depend on hereditary contributions. We associate to the model a nonlinear semigroup and show the behavior of the energy when time goes on. In particular, assuming that the kernels λ and μ decay exponentially, and not too weakly with respect to the physical properties considered in the model, then the energy decays uniformly with respect to the initial conditions; i.e., we prove the existence of an absorbing set for the semigroup associated to the model

Dominantni mod gustoće struje na spiralnoj patch anteni

An elegant and efficient way to calculate and analytically show the main features of spiral patch antennas is presented in this paper. The derivation of an approximate analytical expression for the dominant current density mode on the patch is initially presented, from which it can be easily calculated the patch radiation pattern. Its invariance with frequency scaling, which is the main feature of such log-periodic antennas, is in particular shown, together with a good congruency with experimental results. An extension to higher-order modes for a MoM analysis of the current density is then suggested, which may be useful to study with higher accuracy the other antenna characteristics, such as gain and input impedance at the feed.U radu je prikazan privlačan i djelotvoran pristup proračunu i analitičkom prikazu spiralnih patch antena. Prvo je izveden aproksimativni analitički izraz za dominantni mod gustoće struje na spiralnom patchu. Pomoću izvedenog izraza moguće je jednostavno izračunati dijagrame zračenja patch antene. Proračunom je potvrđeno da se dijagrami zračenja ovakve log-periodičke antene ne mijenjaju s frekvencijom. Utvrđeno je dobro podudaranje proračuna dijagrama zračenja s rezultatima mjerenja. Predloženo je proširenje za više modove gustoće struje pogodne za analizu patch antene pomoću metode momenata. Primjenom metode momenata uz predloženo proširenje višim modovima može se s većom točnošću proučavati i druge osobine antene kao npr. dobitak i ulazna impedancija